Should you turn the HVAC system OFF when gone?

I was recently asked on a Google+ discussion if you should turn your air conditioner OFF when gone. Plenty of room for disagreement even among the professionals. When taking a purely energy conservation viewpoint, you’ll definitely save when using setback periods. However, we buy these HVAC systems for comfort. How comfortable is an 80*F home after climbing from your 65*F car and the 50*F vents blowing on you during your commute? Not really comfortable.

Programmable Thermostat

There’s a simple solution to help – a programmable thermostat with dehumidification capabilities. Research shows use that humans are most comfortable when the humidity is 40-60% and the indoor temperature is 68-78*F. A home at 78*F and 50% humidity has the same comfort feel to most people as a home at 70*F and 60% humidity.

What about dehumidification? Let’s consider the function of an HVAC system in cooling mode. It’s purpose is to cool and remove moisture. If you’re in a deep setup, then the AC won’t be running. If it’s not running, then it’s not removing moisture. So, the programmable thermostats can also dehumidify. They do this by cycling the system for 10 minute periods when there is no active call for cooling.

With that, I recommend a setback similar to the EPA (Energy Star):http://www.energystar.gov/index.cfm?fuseaction=find_a_product.showProductGroup&pgw_code=TH and http://www.energystar.gov/index.cfm?c=thermostats.pr_thermostats_guidelines.

Keys to the savings: setback period should be at least ten hours and 7*F (heating) and 4*F (cooling). Read the footnote on the second link.

 

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